paladin181: I've always enjoyed creating stories and worlds. Then my players try to blow it apart and you have to think on your feet to keep them on the right path. "No, you
can't steal that orb of lucidity from the church, the guards will slaughter you!" I've killed a team of adventurers for that kind of stuff before because they didn't believe I'd kill off their beloved characters... Which really pissed them off but I'm like "Treat your character like a real person. Would an intelligent, sentient being walk into a militant church and steal its prized possession in broad day-light?" Still, I was never invited to be GM for that group again.
I think I only ever wacked a PC twice over the 4 years I've been DM'ing. It should be noted though, that for those 4 years I've only ever DM'ed a band consisting of my 2 best friends, my younger brother and my father (which does not always necessarily make things much simpler).
I have to admitt too we aren't extremely serious roleplayers, or at least not in the beginning. The players simply expect me to offer challenging situation which offer food for thought and much laugther, and they know that every now and then they can try out something drastic (they once set the rich people's district of a city ablaze whilst on a topple-the-evil-government kind of adventure).
I sometimes find it a bit hard to keep the pace flowing coherently though. Every now and then the plot seems to slack away a bit. I can always rely on my players to do some freelance adventuring with more generic "goblin nest clearing" quests while I brew up something more suitably epic though, which is a big boon.
It is for me, as a DM mostly a matter of balancing serious, thought-provoking plots with more light-hearthed combat encounters.